1. Field of the Invention
The present invention relates to a heat treatment apparatus and a heat treatment method.
2. Description of the Prior Art
A vertical heat treatment apparatus is known as one of semiconductor device manufacturing equipment. The heat treatment apparatus is of a batch type of heat-treating many wafers in a batch and a schematic view of a device for performing the vacuum CVD method is shown in FIG. 12. Numeral 1 indicates a wafer boat and the wafer boat 1 holds many wafers W in the terraced state and are transferred into a reaction vessel-composed of a double-structured reaction tube 11 and a cylindrical manifold 12 by an elevator not shown in the drawing. In this case, the reaction vessel is closed air-tightly by a cover 10. The reaction vessel is internally heated by a heater 13 surrounding the reaction tube 11 up to a predetermined temperature and decompressed down to predetermined pressure through an exhaust tube 14. Film forming gas is fed from the lower side of the reaction vessel via a gas feed tube 15, decomposed to thin film components, and deposited on the wafers W and the residual gas is lowered through the space between an inner tube 11a and an outer tube 11b from the ceiling section of the inner tube 11a and discharged through an exhaust tube 14.
Under the wafer boat 1, an insulating unit 16 composed of, for example, quartz fins is installed, and the atmosphere in which the wafers W are placed is insulated from the outside of the cover 10 and kept warm. On the lower side of the wafer boat 1, several dummy wafers W called a side wafer are placed instead of product wafers W.
Meanwhile, the following problems occur in the vertical heat treatment apparatus aforementioned.
(1) To prevent the heat of the atmosphere wherein the wafers W are placed from ejecting from the inside as far as possible, the heat capacity of the insulating unit 16 is set large. Therefore, when the temperature of the treating atmosphere is to be raised up to the target treating temperature and the temperature is to be stabilized, the temperature rise of the insulating unit 16 is delayed and heat is transferred from the treating atmosphere to the side of the insulating unit 16. As a result, the time period required to stabilize the temperature (recovery time) is prolonged, and it causes throughput reduction, and unless a sufficiently long recovery time is taken additionally, the reproducibility for each batch process gets worse.
(2) Since the surface area of the insulating unit 16 is large, the amount of water taken into the reaction vessel via the insulating unit 16 is increased and the water is ejected from the insulating unit 16 during heat treatment and taken into the thin films formed on the wafers W, causing a reduction in the film quality. Before starting the heat treatment, in order to remove impurities such as the water attached to the wafers W, the surface treatment may be performed by flowing, for example, hydrogen gas into the reaction vessel. However, water ejected from the insulating unit 16 is adsorbed to the wafers W, so that the effect of surface treatment is worse.
(3) Furthermore, the film forming gas introduced into the reaction vessel via the gas feed tube 15 passes and rises beside the insulating unit 16. Since the temperature of the insulating unit 16 is low, particularly when the gas flow rate is high, the amount of non-reacted gas reaching the treating atmosphere where the wafers W are placed is increased. As a result, the amount of gas to be decomposed in the treating atmosphere is increased and the generation amount of active species varies with the location, which affects the film thickness of the wafers W. Thus, both the uniformity of film thickness between wafers W and the uniformity of film thickness inside each wafer W are worse.
(4) Although the insulating unit 16 interrupts flowing of heat between the treating atmosphere and the outside of the reaction vessel, the heat dissipation amount on the lower side of the wafer loading area of the wafer boat 1 is large. Thus, side wafers (dummy wafers) have to be placed on several stages of the wafer boat 1 from the lowest stage, thereby the loading area of product wafers W is inevitably narrowed. Therefore, even if the number of wafers to be contained is increased in the wafer boat 1, the number of product wafers W to be processed per a batch process is reduced, and as a result, the improvement of throughput is disturbed.
The present invention was developed with the foregoing in view and is intended to provide a vertical heat treatment apparatus for improving the throughput.
The present invention is a heat treatment apparatus having a reaction vessel with the lower open end, a holding tool contained in the reaction vessel for holding a plurality of objects to be processed, and a cover for blocking the opening at the lower end of the reaction vessel, wherein an insulating unit is provided between the cover and the holding tool, and the insulating unit has a heating unit, and the heating unit comprises ceramics and a heating resistor in the ceramics including few metallic impurities.
The present invention is a heat treatment apparatus that the heating unit is arranged at least either one of the top and side of the insulating unit.
The present invention is a heat treatment apparatus that the insulating unit comprises insulating fins positioned on a side of the heating unit side and heat insulators positioned under the insulating fins.
The present invention is a heat treatment apparatus that the insulating unit comprises a plurality of insulating fins arranged in the horizontal direction.
The present invention is a heat treatment apparatus that the insulating unit is fixed to the cover and the revolving shaft is connected to the holding tool, passes through the through hole of the insulating unit, and is connected to the drive unit.
The present invention is a heat treatment apparatus that the revolving shaft comprises a first revolving shaft passing through the through hole of the insulating unit and a second revolving shaft which is connected to the first revolving shaft through a transmission unit and reaches the drive unit.
The present invention is a heat treatment apparatus that the second revolving shaft passes through the cover and the periphery of the second revolving shaft in the insulating unit passing through the cover is enclosed by a labyrinth having a cover projection extending from the cover and a transmission projection extending from the transmission unit.
The present invention is a heat treatment apparatus that a plurality of supports are arranged on the outer periphery of the insulating unit, at least one support is a tubular one passing through the cover, and an electric feeding line for the heating unit is arranged in the tubular support.
The present invention is a heat treatment apparatus that the heating resistor is made of a carbon material of high purity.
The present invention is a heat treatment apparatus that ceramics are quartz.
According to the present invention, the heat dissipation amount ejected from the treating atmosphere in the reaction vessel to the outside via the insulating unit is reduced, so that the treating atmosphere can be immediately stabilized at the target temperature and the treating area where the temperature is stabilized can be ensured wide. When the insulating unit is structured so as to be fixed to the cover, the electric feed line member can be easily pulled out.
The present invention is a heat treatment method having the steps of holding objects to be processed in a multistage manner by a holding tool, transferring the holding tool holding the objects to be processed into a reaction vessel having a lower open end from underneath, heating the inside of the reaction vessel by a heater installed outside the reaction vessel, feeding film forming gas to said reaction vessel to perform a film forming process to objects to be processed, wherein at the step of feeding film forming gas, a temperature on un under side of the holding tool is higher than that in the atmosphere where the objects to be processed are placed.
The present invention is a heat treatment method that at the step of feeding film forming gas, film forming gas is fed from an under side of the holding tool to the above side of the holding tool and the temperature in the passing area of film forming gas on the under side of the holding tool is higher than that in the atmosphere where the objects to be processed are placed.
The present invention is a heat treatment method that at the step of feeding film forming gas, film forming gas is fed from the above side of the holding tool to the under side of the holding tool.
The present invention is a heat treatment method that the under side of the holding tool is heated by the insulating unit having the heating unit installed under the holding tool and a temperature on the under side of the holding tool is higher than that in the atmosphere where the objects to be processed are placed.
According to the present invention, the decomposition of film forming gas is promoted, so that a process of high uniformity can be performed.